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List:       koffice-devel
Subject:    Re: RFC: Rationalising millimetres/points/inches
From:       Werner Trobin <trobin () kde ! org>
Date:       2001-02-22 18:19:42
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David Faure wrote:
> 
> On Thursday 22 February 2001 17:14, Werner Trobin wrote:
> > Ehrm... sorry to be pedantic, but pt <-> mm is always the same,
> > but pt/mm <-> pixel changes depending on the resolution.
> 
> Ok, I had a doubt about whether I knew what pt means. It appears I don't.
> Can you enlighten me ? :-)

Well... I think I know, but there are some doubts here and there.
Let's see whether is makes sense in the end:
Years ago, when printers used real "letters" to typeset books and
so on they had an interesting ammount of units. E.g. "Pica - a
printing industry unit of measurement. There are 12 points to a pica,
one pica is approximately 0.166in". And of course "Point - the standard
unit of type size of which there are 72 to the inch (one point is
approximately 0.01383in). Point size is the measured from the top of the
ascender to the bottom of the descender."
(see http://www.sos.com.au/files/glosray.html)

For the ultra pedantic ones - this is not the whole truth. There are
at least ten different "points" (for your amusement I'd suggest
visiting http://www.vakcer.com/oberon/dtp/fonts/point.htm :)

However, we use the 1/72 definition. This is just a factor between
inch and point. There's no point (pun intended :) in assuming that
one point equals one pixel on the screen, though. The relation
in/mm/pt <-> pixel depends on the resolution of your monitor (which
is given in DPI (dots per inch) normally). On Windows (and with
XFree86 > 4) the default resolution is 96 dpi, however, one can
specify a -dpi option for the X server, or it's not configured
correctly, or... To make a long story short: The resolutions seem
to vary in a range of about 75 to 120 dpi. Note that sometimes the
X and Y resolution are not equal. TrollTech decided to use only
the Y resolution to select fonts and stuff. Therefore I suggest
also doing so.

I hope this clarifies a few things. :)

-- 
Werner Trobin - trobin@kde.org
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